Method and apparatus for detecting leaks

ABSTRACT

A leak detection method and apparatus is characterized by the production of analog signals representative of the fluid inlet flow and fluid outlet flow of a closed or open system. The signals are compared, and a difference signal is generated which is a function of changes in the flows. This signal is processed to provide an indication of a leak within the system. By processing the analog signals, more accurate measurement of fluid differential, and thus fluid leakage, is obtained.

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/707,484 filed Nov. 7, 2000, now U.S. Pat. No. 6,481,265.

BACKGROUND OF THE INVENTION

In all industries, there are closed circuit systems in which fluidinflow and outflow are monitored in order to discover leaks. Typicalexamples of these are closed cooling water systems or hydraulic systems.In many systems of this type, even small leaks can have devastatingconsequences. For example, in the cooling water systems of variousmelting furnaces, a very small leak allows water to penetrate into themelt, thereby causing serious explosions. Accordingly, the detection ofthis type of leak is of great importance. Similarly, open circuitsystems such as flow channels may also contain leaks.

BRIEF DESCRIPTION OF THE PRIOR ART

It is known in the art to separately measure the inflow and outflow ofboth closed and open systems and then calculate the difference betweenthe two to obtain an indication of a fluid leak in the system. If thereare no leaks, the difference is zero.

Since the flow measurements usually involve large values, it isdifficult to determine small differences owing to limitations in theaccuracy of the measuring equipment and techniques of the prior art. Thepresent invention was developed in order to overcome this drawback byproviding a more accurate process for detecting leaks, and particularlysmall leaks, in a both closed and open circuits.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the invention to provide a methodand apparatus for detecting fluid leakage in closed and open systemswherein the fluid input and output of the system are measured and analogsignals corresponding to the measured values are produced and comparedto provide a difference signal. The difference signal is processed andthe output indicates the severity of a fluid leak. If the differencesignal is zero, then there are no leaks in the system.

According to a more specific object of the invention, a calorimetricmeasuring system is used to measure fluid input and output. Acalorimetric system is one which is based on heat dissipation. Theanalog signals are compared in a bridge circuit to produce thedifference signals. Accordingly, even a very small difference betweenthe analog signals creates a significant output signal resulting in ahigh sensitivity in leak detection.

According to a further object of the invention, a threshold level forthe difference signal is established and when the threshold is exceeded,corrective action may be taken to prevent damage to the system.

BRIEF DESCRIPTION OF THE FIGURES

Other objects and advantages of the invention will become apparent froma study of the following specification when viewed in light of theaccompanying drawing, in which:

FIG. 1 is a schematic view of the leak detection apparatus according tothe invention;

FIG. 2 is a circuit diagram of a first embodiment of the measuringsystem of the invention of FIG. 1; and

FIG. 3 is a circuit diagram of a second embodiment of the measuringsystem of the invention of FIG. 1.

DETAILED DESCRIPTION

Referring first to FIG. 1, the leak detection method and apparatusaccording to the invention will be described. A closed or open system 2has a fluid inlet 4 and a fluid outlet 6 in which flow sensors 8, 10 arearranged. The flow sensors are separate elements of the same type andproduce analog signals in accordance with the fluid flow being detectedat the inlet and outlet, respectively. These analog signals are sent toa comparator 12 which determines the difference between the analogsignals. The comparator produces a difference signal which is deliveredto a signal processor 14. The processor produces an output signal whichis a function of the fluid leakage from the system 2. If there is noleakage, the difference signal is zero. Based on the output signal, anindication of the severity of a leak is provided. The signal processorcan also establish a threshold level for the difference signal. If thedifference signal exceeds the threshold, then emergency action such asshutting down the system may be taken to prevent damage thereto. Thiscan be done manually or automatically. In an automatic mode, the signalprocessor issues a switching signal to curtail or shut down the system.

In the embodiment shown in FIG. 2, a calorimetric (heat dissipation)technique for detecting leaks is shown. More particularly, each sensor8, 10 comprises a thermistor including an electric heating element 16,18 and a variable resistor 20, 22. The thermistor can be either a PTCresistor or an NTC resistor. The heating element elevates thetemperature of the thermistor above the temperature of the fluid whoseflow is being measured. The cooling effect on the thermistor of thefluid is a function of the flow rate. That is, the temperaturedifferential between the thermistor and the ambient fluid diminishes asa function of the fluid flow rate.

The flow sensors 8, 10 are electrically connected in a bridge circuitwith the sensor elements of the two lines forming one leg of the bridge.Resistors 24, 26 are also connected in the bridge circuit. As long asthe inlet flow and the outlet flow are equal and no leaks are present inthe system, the resistances of the sensors 8, 10 are equal. The bridgecircuit is thus balanced and the bridge voltage measured at theterminals U is zero. However, if the inlet and outlet flows are unequal,the resistances of the sensors are also unequal and the bridge voltagehas a value corresponding with the difference between the resistanceswhich in turn is a measure of the disparity in flow rates.

The sensor arrangement shown in FIG. 2 is for situations where thetemperature of the fluid at the inlet 4 and outlet 6 of the system isthe same. In reality, the temperatures are rarely the same. Accordingly,it is necessary to compensate for the temperature differential. In theembodiment of FIG. 3, each sensor 8, 10 includes an unheated variableresistor 28, 30 which is used to measure the temperature of the fluid.With this determination, the temperature variation in the fluid can beeliminated from the flow detection process so that the bridgemeasurement at the terminals U is independent of fluid temperature.

The principle of flow measurement with constant heating of thethermistors described above with reference to FIG. 2 is very simple andis accurate only in connection with low flow rates. For measurement ofhigher flow rates, there are other calorimetric or heat dissipationprinciples of measurement which can be used. For example, the elevatedtemperature may be held constant by a control circuit. Alternatively,heat is supplied to the thermistors in pulses and the difference signalis derived from the heating or cooling time. These principles ofmeasurement for leakage detection can also be applied to othercalorimetric measuring processes.

Other principles of flow measurement may also be used. For examplepressure differentials between inlet flow and outlet flow ormagnetic-inductive principles of measurement can be used to convert theflow to be measured into analog signals. These signals can then becompared as in the calorimetric techniques described above.

While the preferred forms and embodiments of the invention have beenillustrated and described, it will be apparent to those of ordinaryskill in the art that various changes and modifications may be madewithout deviating from the inventive concepts set forth above.

What is claimed is:
 1. A method for detecting fluid leakage in an opensystem comprising the steps of (a) measuring the fluid input and thefluid output of the open system using a calorimetric system andproducing analog signals corresponding to the fluid input and fluidoutput; (b) comparing the fluid input analog signal with the fluidoutput analog signal in a bridge circuit adjusted to zero voltage undera no leak condition to produce a difference signal; and (c) processingsaid difference signal to compensate for a temperature differencebetween the fluid input and the fluid output and to provide anindication of fluid leakage from the open system, said difference signalbeing zero when there is no fluid leakage, whereby minute leakage levelsare detected and measured in accordance with said difference signal. 2.A method as defined in claim 1, wherein said processing step comprisesone of analog and digital processing.
 3. A method as defined in claim 2,and further comprising the steps of establishing a threshold level forsaid difference signal and detecting when said difference signal exceedsthe threshold level.
 4. Apparatus for detecting fluid leakage in an opensystem, comprising (a) a first thermistor arranged in a fluid inlet tothe system for generating a first analog signal corresponding to thefluid input; (b) a second thermistor arranged in a fluid outlet from thesystem for generating a second analog signal corresponding to the fluidoutput; (c) a first temperature compensation device arranged in a fluidinlet to the system for generating a third analog signal correspondingto the temperature of the fluid input; (d) a second temperaturecompensation device arranged in a fluid outlet from the system forgenerating a fourth analog signal corresponding to the temperature ofthe fluid output; (e) a bridge circuit wherein said first and secondthermistors comprise first and second legs thereof, and said first andsecond temperature compensation devices comprise the third and fourthlegs thereof, said bridge circuit being adjusted to zero voltage under ano leak condition and comparing said first and second analog signals toproduce a difference signal; and (f) means for processing saiddifference signal to provide an indication of fluid leakage from theopen system, said difference signal being zero when there is no fluidleakage, whereby minute leakage levels are detected and measured inaccordance with said difference signal and temperature variations in thefluid are eliminated.
 5. Apparatus as defined in claim 4, wherein saidthermistors comprise a heating element and a variable resistor, saidvariable resistor having a resistance value which changes as a functionof fluid flow.
 6. Apparatus as defined in claim 4, wherein each of saidtemperature compensation devices comprises a second variable resistorspaced from said beating element.